Defending champion Usain Bolt of Jamaica overcame an early stumble to advance to the final of the 100 metres at the world championships on Sunday.
Bolt rode through the early scare after a terrible start to turn on the power in the final 40 metres and clock 9.96 seconds, with Canadian Andre de Grasse second on the same time.
American rival Justin Gatlin, who has twice served bans for doping, had no such problem in the second heat, winning in a blistering time of 9.77 ahead of compatriot Mike Rodgers, who has also served a drugs suspension.
A third American, Tyson Gay, the 2007 double world sprint champion and also a convicted drugs cheat, won the final heat in 9.96 ahead of Jamaican Asafa Powell, the self-proclaimed "king of the sub-10" in 9.97.
It was the 93rd time Powell, who served a six-month ban for doping after a positive test saw him miss the 2013 worlds in Moscow, has dipped under the once-mythical 10 second barrier.
Also qualifying as the three fastest other times were American Trayvon Bromell and China's Bingtian Su, who both timed 9.99 in Bolt's opening heat, and Frenchman Jimmy Vicaut, who clocked the same time in Gay's heat.